The invention disclosed in this application is directed generally to the cleaning and handling of particulate materials, such as plastic pellets, grains, glass, and the like, and particularly to the cleaning of particulate injection moldable materials as close to the actual molding process step as possible to significantly reduce contaminants.
It is well known, particularly in the field of transporting and using particulate materials, commonly powders, granules, pellets, and the like that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, and streamers (ribbon-like elements that can xe2x80x9cgrowxe2x80x9d into quite long and tangled wads that will impede the flow of materials or even totally block the flow). The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants.
The term xe2x80x9ccontaminantxe2x80x9d as used herein includes a broad range of foreign material as well as the broken particles, dust, fluff and streamers mentioned in the preceding paragraph. In any case, contaminants are detrimental to the production of a high quality product, and in some situations a health risk to employees of the producer and possibly even a source of danger in that some contaminants can produce a dust cloud which, if exposed to an ignition source, may explode.
Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and are, therefore, unsellable. It is important to note that since these same non-uniform materials often do not melt at the same temperature as the primary product, the unmelted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and thus increased overall production costs.
Since dust and other contaminants are generated mostly by the transport system, it is of primary importance to not only provide apparatus for thoroughly cleaning the particles, but to do so as close to the point of use of the particles as possible so as to avoid the generation of contaminants through additional transport. Dedusters have been used for several years to clean materials in this application; however, the instant invention provides a large improvement over the prior art. Applicants identified the need for a smaller more compact deduster, capable of handling smaller volumes of product, yet also capable of thoroughly cleaning the product. Importantly, that the instant invention significantly reduces size and costs over prior similar machines and permits installation in the material handling process immediately before final use of the products rather than at an earlier stage after which re-contamination can occur.
In the past, larger dedusters were used to clean product that was then stored in bulk for later use in molding. The stored material was then often sent through a dryer to eliminate moisture just before injection molding. Moisture on the plastic pellets becomes steam in the molding machine, resulting in bubbles or discoloration in the final product. The more significant problem faced under the old system was that after cleaning and bulk storage, the particles had to be transported to the dryer, creating new dust and picking up new contaminants inherent in transport-so when the product reached the dryer, the dust and other contaminants would be xe2x80x9cbakedxe2x80x9d on the pellets due to the high temperatures required for drying. Such problems make evident the value of cleaning just prior to drying and molding. With this new design, manufacturers will experience reduced scrap, improved end product quality, decreased maintenance on machinery, increased productivity, and short investment paybacks.
It is an object of the invention to overcome the disadvantages of the prior art by providing a compact dedusting apparatus that is capable of handling volumes of particulate material for feeding to a molding machine, while thoroughly cleaning the material before being used by the machine.
It is another object of this invention to provide an effective compact dedusting apparatus that can be thoroughly clean a flow of particulate material of dust particles and other contaminants immediately prior to the particulate material being used.
It is an advantage of this invention that the particulate material is not subjected to subsequent contamination after being cleaned through storage and handling operations.
It is a feature of this invention that the compact deduster can be mounted on a plastic molding machine to cleanse plastic pellets of contaminants as the pellets are being fed into the molding machine.
It is still another object of this invention to provide a metering apparatus that is effective to constantly meter the flow of particulate material through the dedusting apparatus.
It is another feature of this invention that the metering apparatus is formed as a rotatable finned hub that blocks an opening through the dedusting apparatus to control the flow of particulate material through the opening.
It is still another feature of this invention that the finned hub is rotated at approximately one revolution per minute.
It is another advantage of this invention that the finned hub utilized flexible blades that will deflect when encountering a material clog to maintain a uniform constant flow of particulate material through the deduster apparatus.
It is yet another object of this invention to connect the dedusting apparatus to a remote dust collector apparatus that provides a flow of clean air through the dedusting apparatus.
It is yet another feature of this invention that the air flow through the dedusting apparatus is directed in multiple paths, including a path that creates an air knife to help dislodge contaminants from the particulate material being cleansed by the deduster apparatus.
It is a further feature of this invention that the infeed device directing particulate material through the dedusting apparatus is formed as an angled chute with an opening at the lower portions of the chute to direct the flow of particulate material through the dedusting apparatus.
It is still another advantage of this invention that the metering device is rotatably mounted at a position over the opening at the bottom of the infeed chute directing the flow of particulate material through the dedusting apparatus.
It is still a further feature of this invention that the angle of the blades on the finned hub is oriented at an angle to the slope of the infeed chute to facilitate the flow of particulate material into the opening in the infeed chute.
It is yet another advantage of this invention that a magnetic flux field can be utilized to disrupt the electrostatic bond between the particulate material and the contaminants clinging thereto.
It is a further object of this invention to provide a compact dedusting apparatus that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use.
These and other objects, features and advantages are accomplished according to the instant invention by providing a compact dedusting apparatus that can be mounted on the machine utilizing particulate material requiring contaminant cleansing to provide an economical and effective decontamination of particulate material immediately before utilization of the material. The dedusting apparatus includes a downwardly sloped infeed chute having an opening at the bottom thereof. A metering device in the form of a rotatable finned hub blocks the opening to constantly meter the flow of particulate material through the dedusting apparatus. The metering device is formed with flexible blades oriented at a slight angle to the slope of the infeed chute to provide a constant flow of material through the opening. A flow of air is directed through a wash deck positioned below the infeed chute to cleanse the particulate material. The air flow is directed along multiple paths including a path defining an air knife associated with the wash deck to facilitate the cleansing of the material. After passing through the dedusting apparatus, the particulate material is fed directly to the machine utilizing the material.